In a small bowl, combine sugar and seeds from the vanilla bean.
Using the back of a spoon, move around the bowl and apply pressure to break up any clumps of seeds and to better infuse the vanilla flavor into the sugar. Set aside.
In a medium-sized mixing bowl or bowl of a stand mixer, mix together cake flour, baking powder, baking soda, and salt.
Add the vanilla bean sugar and mix until well combined.
Add butter and mix on medium-low speed for three minutes. Because there is so little butter, you'll end up with a very fine crumb texture.
In a small mixing bowl, whisk together eggs, sour cream, oil, and vanilla extract until smooth.
Add the egg mixture to the flour mixture and beat on medium speed until just combined.
Slowly add milk and mix on low speed until just combined. The batter will be liquid. (Don't worry, you didn't do anything wrong. It's supposed to be that way.)
Fill a single cupcake liner just over 1/2 full. Bake for 14 minutes and then test to see if it's done. It's done when a toothpick comes out without wet batter stuck to it. The cupcake should appear white with specks of vanilla bean. It should not turn a golden brown. If it is not done, test again in two minutes. If it is still not done, test again in another two minutes. When the cupcake is done, remove it immediately from the tin and leave it on a cooling rack (or just on your counter if you don't own a cooling rack) to cool.
Fill the remaining cupcake liners 1/3 full with batter. There should still be some batter left over.
In a medium-sized mixing bowl, mix butter and cream cheese until light and fluffy (about three minutes at high speed).
Mix in powdered sugar a little at a time.
Mix in strawberry powder and salt.
Cake Mixture Instructions
Remove cooled baked cupcake from the liner and break into crumbs.
Mix crumbs with 2 teaspoons of the frosting until it forms a Play-Doh-like consistency.
Mix in the strawberry powder until the cake mixture becomes a color that you like.
Cupcake Instructions, Part Two
Rip off pieces of the cake mixture and sculpt into the shape illustrated in this post - a small ball with a bowl on top that is just big enough to rise slightly above the batter.
Place the ball/bowl shape in the center of each filled cupcake liner.
Fill each bowl with a small dollop of batter.
Bake for 20 minutes or until the cupcakes bounce back when lightly touched.
The cupcake batter should have risen enough to completely hide the bunnies.
Remove cupcakes from the tin and set on a cooling rack or the counter to cool.
Pipe strawberry frosting onto cooled cupcakes.
Serve with a knife and instructions to cut each cupcake open down the center. If people just bite quickly into the cupcakes, they will miss the surprise!
I highly recommend that you do one or two test cupcakes to get the knack of this before baking all of the batter. It can take some tweaking to make the bunny the perfect size and to get the batter to rise just the right amount.